Development of a commercially successful ophthalmic device formed from traditional silicone hydrogel materials frequently requires post cure generation of a wettable surface. Traditional silicone hydrogel contact lenses may demonstrate surfacing of silicone chains, i.e., silicone rich domains residing on the surface of a lens. Surfacing of silicone chains can create hydrophobic areas on the lens surface. These surface hydrophobic areas may adversely impact lens wettability. Post cure treatment of the lens surface to enhance wettability is effective but expensive; the additional step(s) add cost and time to the manufacturing process. An alternative to post cure treatment of the surface is incorporation of polyvinylpyrrolidone (PVP) of relatively high molecular weight (for example >300 kDa) into the device by adding it to the monomer mix before curing. The resulting material has entangled non-covalently incorporated PVP which, because of its high molecular weight, will not easily leach out of a hydrated lens. Other methods of providing hydrophilic polymers in the device of a polymerized device are still needed.
Incorporation of substantial amounts of relatively slow reacting hydrophilic monomers such as N-vinylpyrrolidone (NVP) along with faster reacting comonomers in the monomer mix may create a successful ophthalmic device by formation of chains of primarily homo-polyvinylpyrrolidone (PVP) in situ as the device cures. However, monomers typically found in ophthalmic device forming monomer mixes may include relatively slow reacting monomers such as NVP, O-vinyl carbonates, O-vinyl esters (e.g. vinylacetate), O-allyl esters, O-allyl carbonates and N-vinyl carbamates, as well as relatively faster reacting monomers such as acrylates, methacrylates, acrylamides, methacrylamides and styrenics. In device forming systems containing mixtures of fast and slow reacting monomers (such as may be found in monomer mixes for forming silicone hydrogels) a difference in the reaction kinetics of the device forming system (e.g., addition to C═C vs. hydrogen atom transfer) makes such systems particularly susceptible to incomplete cure. Therefore, the relatively sensitive kinetics of the curing reaction in these device forming systems makes creating a successful ophthalmic device difficult.
U.S. Pat. No. 5,135,965 discloses certain monomer mixes containing N-vinylpyrrolidone (NVP) and UV-absorbers capable of being bound to the device after reaction and extraction for intraocular lens applications. The formulations disclosed in U.S. Pat. No. 5,135,965 are not silicone hydrogels.